A cylinder lock is a lock constructed with a cylinder that is able to rotate with respect to a housing along a so-called shear line, however in principal only when a corresponding key (or at least the blade thereof) is placed in the keyway. The housing is stationary with respect to the door or other item that can be locked. The cylinder by rotating, optionally by actuating a cam, is used to change the position of the actual locking element such as a bar of metal that actually secures the position of the element to be locked (typically a door). A locksmith can easily unscrew the cylinder to facilitate rekeying. The cylinder may contain any of a variety of locking mechanisms, including commonly known mechanisms such as the pin tumbler lock, the wafer tumbler lock and the disc tumbler lock. Any of these locks may be designed for any known type of key such as a cut key (having saw tooth like bitings), a dimple-key, tubular key (for so called radial locks), skeleton key, Zeiss key (also known as cruciform key), Abloy key, magnetic key etc. These keys may be single- or multiple sided as known in the art.
The first main advantage to a cylinder lock, also described as a profile cylinder lock, is that the cylinder may be changed without altering the boltwork hardware. Removing the cylinder typically requires only loosening a set screw, then unscrewing the cylinder from the boltwork. The second is that it is usually possible to obtain, from various lock manufacturers, cylinders in different formats that can all be used with the same type of key. This allows the user to have keyed-alike, and master-keyed systems that incorporate a wide variety of different types of lock, such as night latches, deadbolts and roller door locks. Typically, padlocks can also be included, although these rarely have removable cylinders. Standardised types of cylinder include key-in-knobset cylinders, rim (also known as night latch) cylinders, Ingersoll format cylinders, American, and Scandinavian round mortise cylinders, and Scandinavian oval cylinders. There are also standardised cross-sectional profiles for lock cylinders that may vary in length—for example to suit different door thicknesses. These profiles include the europrofile (or DIN standard), the British oval profile and the Swiss profile.
Cylinder locks however are vulnerable to forced entry by various techniques used in the art of burglary and law enforcement. Conventional cylinders can be easily drilled to create another shear line to allow the cylinder to turn freely without a key or to totally remove the internal components of the cylinder, whereafter a screwdriver can be used to rotate the cam. Another technique aims at pulling a cylinder from its housing. In this technique a special hardened screw is inserted into the keyway, and then an extreme pulling force is applied with a tool to exert reverse pressure against the door. This is a simple technique for which even commercial sets are available. Yet another technique is commonly referred to as a twisting attack. This technique relies on torsion and twisting forces that can be applied to a screwdriver or alike that is inserted deep enough into the keyway. A torque as great as 600 pound-inches can be easily applied by using a common adjustable wrench. This way, the lock can be broken allowing removal of the cylinder.
Yet another commonly applied technique uses a co-called bumpkey to bump a lock. When bumping a lock, a key that mechanically fits the key way such that it can at least be inserted in the cylinder, is initially inserted into the keyway one pin short of full insertion. Bumping the key inward forces it deeper into the keyway. The specially designed teeth of the bump key transmit a slight impact force to all of the bottom pins in the lock. The key pins transmit this force to the driver pins; the key pins stay in place. Because the pin movements are highly elastic, the driver pins “jump” from the key pins for a fraction of a second, moving higher than the cylinder (i.e. the shear line), then are pushed normally back by the spring to sit against the key pins once again. Even though this separation only lasts a split second, if a light rotational force is continuously applied to the key during the slight impact, the cylinder will turn during the short separation time of the key and driver pins, and the lock can be opened while the driver pins are elevated above the keyway. Lock bumping takes only an instant to open the lock and the lock is usually not visibly damaged.
Impressioning is yet another non-destructive, covert method of creating a working key for a lock without picking or disassembly. Impressioning is one of the most useful skills in locksmithing, and is divided between copying and manipulation techniques. Copying focuses on making negative-image moulds of a source key, while manipulation uses various techniques to determine the proper heights of internal components without the source key being available. For the latter method, it is needed that a blank key is slided into the key. Impressioning via manipulation is closely related to decoding. Many high profile crimes have been accomplished through the use of impressioning techniques.
Pin tumbler locks are vulnerable to lockpicking. This technique involves a pick, which is a thin piece of hard steel with a small hook at its end, and some other tool (typically a tension wrench) that can be inserted into the keyhole alongside the pick and used to rotate the cylinder. The technique relies on small imperfections in the cylinder, that lead to a single pin holding the cylinder from rotating. The burglar applies a constant (though weak) torque on the cylinder with a wrench, and tries the pick at each pin.
When the pick fiddles with the pin that actually holds the cylinder, the cylinder will rotate minutely, until another pin will stop it. Now the first pin is held in open position by the cylinder itself, and the burglar can proceed to pick the other keypin. Though these principals are easy to understand, in practice a great deal of experience and patience is required in order to master this technique. Very high quality cylinders are less prone to this attack, requiring more time as well as superior skill, however, electronic locks are far cheaper and robust just as well.
Manual and electronic pick guns are a popular method used today for quick and easy ways of opening doors. The higher-end electric pick guns are usually made of aircraft aluminum and hard steel. The pick is operated by simply pressing a button that vibrates while the normal tension wrench is being used. A manual pick gun (or Snap gun) is used in a similar way but usually has a trigger that creates a movement which (like bump keys) operates on the same principle as Newton's cradle. It transfers sudden energy to the key pins which communicate this to the driver pins causing those pins only to jump, allowing the cylinder to turn freely for a brief moment, until the pin springs return the pins to their locking position. A pick gun is used in conjunction with a tension tool and the only skill required here is learning the timing.
Various locks with additional means to protect the lock against forced entry have been described in the art.
GB 775,098 shows a pin tumbler lock with an additional security feature in the form of a plunger normally resiliently loaded to an unlocking position where it is housed within the cylinder but axially movable from said unlocking position to a locking position bridging the housing and the cylinder, by plunger operating formations on the side of the key. This includes a bevelled side face on the leading end of the key adapted to engage the plunger and move it to a locking position.
U.S. Pat. No. 4,490,998 describes a tamper resistant cylinder lock including a pair of cooperating keyway guard plates, each of which has a keyway formed therethrough. The guard plates are laterally displaceable relative to one another for movement between an open position in which the keyways of the guard plates are aligned to allow for passage of a key, and a blocked position in which the keyway of one of the guard plates is at least partially blocked by the other one of the plates. A uniquely configured key is needed for use in combination with such guard plates.
Likewise, FR 2785322 discloses a tamper resistant cylinder lock including a pair of cooperating keyway guard plates, each of which has a keyway formed therethrough. The configuration of one of the guard plates is controlled using a configuration mechanism that is controllable by wireless communication between the lock and a remote control unit.
U.S. Pat. No. 7,673,484 discloses a pin tumbler lock which in addition to the pin tumbler locking means, is provided with a block assembly to prevent the cylinder from rotating with respect to the housing. This provides additional means for preventing the lock to be tampered.
DE 10 2004 055979 discloses a cylinder lock which in addition to the commonly known multiple locking pins to prevent rotation of the cylinder in the housing, which elements can be controlled by inserting a fitting key, has an extra locking pin to prevent rotation of the cylinder in the housing. This additional pin can be controlled via wireless communication. This way, the insertion of a (mechanical) fitting key alone in the keyway is not sufficient to allow rotation of the cylinder in the housing, a further actuation is needed to retract the additional element from its blocking position into a position where rotation of the cylinder is allowed. This way, although the entry of a non-allowed key cannot be prevented, even if this non-allowed key is fully inserted in the keyway, the rotation of the cylinder will still be blocked if the required further actuation of the additional locking pin is not provided.